I had the same situation as jocelyn at the top of this thread. I'm running 7.0, and deferred once right before I shutdown. From then on, proactive backups were not working. I turned off the warning notification and then it executed -- not before I uninstalled and reinstalled the client a few times. This would be a good knowledgebase article. Additionally, I'm curious as to what could possibly be causing this. I'm thinking about turning the warning notification on one more time to see if it will work.